Pregnant women and newborn infants will be followed to detect and measure group B streptococci, an important cause of newborn infections. The purpose is to understand the epidemiology and carriage of this bacterium, particularly with reference to the gastrointestinal tract. Healthy adult volunteers will be studied to locate the sites of streptococcal carriage in the gastrointestinal tract. Patients and their contacts will be studied in a venereal disease clinic to evaluate the importance of sexual transmission in streptococcal spread.